1. Field of the Invention
The present invention relates to a sound signal playback machine and method thereof for playing back multichannel sounds.
2. Description of the Related Art
Concerning the sound signal playback machine for playing back multichannel sounds, for example, a sound signal playback machine to realize 5.1 surround playback is well known. FIG. 10 is a block diagram showing an example of such a sound signal playback machine. In FIG. 10, the signal input terminal 101, to which sound signal SL of L-channel (left channel) is supplied, is connected to the speaker 131, which is arranged at the front on the left, via HPF (high-pass filter) 111 and the amplifier 121. At the same time, the signal input terminal 101 is connected to the signal adder 151 via LPF (low-pass filter) 141. The signal input terminal 102, to which sound signal SR of R-channel (right channel) is supplied, is connected to the speaker 132, which is arranged at the front on the right, via HPF 112 and the amplifier 122. At the same time, the signal input terminal 102 is connected to the signal adder 151 via LPF 142. The signal input terminal 103, to which sound signal SSL of SL-channel (surround left channel) is supplied, is connected to the speaker 133, which is arranged at the rear on the left, via HPF 113 and the amplifier 123. At the same time, the signal input terminal 103 is connected to the signal adder 151 via LPF 143. The signal input terminal 104, to which sound signal SSR of SR-channel (surround right channel) is supplied, is connected to the speaker 134, which is arranged at the rear on the right, via HPF 114 and the amplifier 124. At the same time, the signal input terminal 104 is connected to the signal adder 151 via LPF 144. Further, the signal input terminal 105, to which sound signal SC of C channel (central channel) is supplied, is connected to the speaker 135, which is arranged at the front center, via HPF 115 and the amplifier 125. At the same time, the signal input terminal 105 is connected to the signal adder 151 via LPF 145. On the other hand, the signal input terminal 106, to which sound signal SLFE of LFE channel (channel exclusively used for the low frequency band) is supplied, is connected to the signal adder 152 to which the above signal adder 151 is connected. This signal adder 152 is connected to the speaker 136, which is arranged on the side, via the amplifier 126. In this case, the speakers 131 to 135 respectively compose a speaker system for playing back sounds of middle low frequency and higher frequency than that. In general, they are referred to as a satellite speaker system. The speaker 136 is a speaker system for playing back sounds of low frequency. In general, the speaker 136 is referred to as a sub-woofer.
In this connection, the above conventional sound signal playback machine is designed so that the frequency response can be flat when signals on the low frequency side and those on the high frequency side are electrically synthesized with each other. Further, in the above conventional sound signal playback machine, it is necessary to use a filter of the high order so that the band width, in which the frequency response on the low frequency side and that on the high frequency side cross each other, can be reduced. Accordingly, the following problems may be encountered. The frequency response of signals, which are obtained when signals on the low frequency side and signals on the high frequency side are electrically synthesized with each other, are flat as shown in FIG. 11, however, as shown in FIG. 12, a group delay in the low frequency band is increased, which causes such a problem that sounds of low frequency can not be faithfully played back and further a nuance of sounds of a musical instrument of low frequency is changed. In the case where sound signal SLFE of channel LFE and sound signals SL to SC of the other channels (main channels) are correlated with each other, a group delay is increased in the low frequency band when sound signal SLFE in channel LFE is added.